Japan Whips Incumbents

Vote Could Present Challenges for Obama Administration

TOKYO—Voters handed a stunning rebuke to the ruling Democratic Party of Japan, just 10 months after giving the party the keys to government in a historic transfer of power.

Sunday's vote seems likely to usher in a new period of political instability in Tokyo, making it difficult for Prime Minister Naoto Kan to move forward on key policy matters, such as curbing the government's massive outstanding debt to prevent a Greece-style...